1. Field of the Invention
The present invention is related generally to the decontamination of fluids and in particular, to the removal of grease or oil from water.
2. General Background
In the offshore oil and gas production industry, water (produced-water) is produced with oil. As a result of such production of oil and water, the water is often contaminated with oil. Present U.S. Environmental Protection Agency (EPA) interim guidelines on offshore produced-water treatment and disposal require that less than forty-eight (48) ppm of effluent-oil concentration must be present in produced-water prior to disposal into the surrounding offshore waters. This makes it desirable and necessary to improve the quality of such produced-water prior to disposal.
Various treatment techniques used in the industry include: free-water knockout (FWKO), skim tanks, plate coalescers, skim piles and flotation units, particularly flotation separators using multi-stage gas-air eductors or vigorous mixing of produced-water with gas-air to form a froth to float the oil to the surface for skimming and leaving a water with some oil contaminants.
Devices and methods addressing the above problems of which applicant is aware include the following:
U.S. Pat. No. 4,627,922 to Viator, et al. (the applicant was a co-inventor) entitled "Method Of Removing Dissolved Oil From Produced Water" discloses a method of removing dissolved oil from produced water by turbulently contacting gaseous dichlorodifluoromethane ("Freon 12") with the water to create bubbles that move dissolved oil particles to the surface of the water and removing freed dissolved oil from the surface. This method teaches neither absorption to remove oil from produced-water nor a reclaiming step as taught by applicant, but rather a "flotation" or ionic effect to break the bonds solvating the oil to separate it.
U.S. Pat. No. 4,060,912 entitled "Absorber-Contactor" discloses a system for removing contaminants, such as vapors and condensibles, from gas which includes a tortuous or spiral path-forming container wherein the contaminated gas is caused to repeatedly pass through a layer of absorbent fluid.
U.S. Pat. No. 4,094,783 entitled "Centrifugal Flotation Separator" issued to G.F. Jackson discloses a multi-stage, recycling, centrifugal flotation separator system. A closed circular cylindrical vessel has a tray or baffle positioned inside the vessel near the top with an axial opening for the upward flow of froth and gas bubbles. Contaminated liquid and air under pressure are introduced into the vessel through tangential pipes to form bubbles. Gas released at the top of the vessel and liquid from the bottom zone are recycled into the vessel. The clean liquid is drawn from the bottom of the tank close to the outer wall.
U.S. Pat. No. 3,542,675 entitled "Water Treatment" issued to I.P. Mail, et al. discloses the flowing of liquid saturated with gas into a container and through a venturi structure which reduces the pressure on the saturated liquid to enable gas bubbles to form. The flow rate of the gasified liquid is controlled to maintain a pre-determined ratio to the flow rate of the contaminated liquid flowing through the container.
While the above have demonstrated a certain degree of effectiveness in removing oil contaminants, a higher degree of efficiency has been sought in the industry.